In the compatibility mode, ASDlite accepts all the above forms of
operations and designators.

Dependencies in ASDlite

An action is a pair of an operation and a component. Some
actions modify the file system, whereas other actions modify the current image,
and this implies a difference in how to interpret timestamps.

Dependencies (rules) between actions are stored in each (target)
component and represented by the two alists of target operations to other (dependee)
actions.

There are two kinds of rules.

caused-by (named "in-order-to" in ASDF)

If any of dependee actions are already in the current plan
(as its results have become out-of-date according to timestamp
or as a result of other rules executing successfully), that triggers
this rule, i.e. the target action is also placed into the plan.

requires (named "do-first" in ASDF)

These dependee actions have to be planned before the operation on
the target component. But they do not trigger this rule per se,
i.e. re-performing the target operation.

Example

If B has changed, B.fasl needs to be recompiled. So the caused-by rule
triggers recompiling of A.fasl irrespective of whether A has itself changed.

If A has changed, this neither imply compiling B nor C. But due to the
requires rule loading B.fasl must be in the image precede compiling A.

CAUTION:
A component is only allowed to depend on its siblings, i.e. the componentsof the same module, no mater how we define dependencies:

either :depends-on option,

or operation-caused-by/-requires method.

Observation and rationale

The ASDF built-in operation hierarchy is actually of two-level depth.
The original ASDF code does not exploit operation inheritance much (though
something can be found in asdf-ecl.lisp).

The operation slots are rather useless:

original-initargs

Is only referred in print-object

parent

In principle, indicates the target operation that required this one.But due to reusing operation objects in
make-sub-operation, this is not the case.
Also used for marking along with other visiting slots during traverse but we follow another approach.

Adding entirely new operations, i.e. on the first level, is fine. But there is comfortable way to refine existing operations: the easiest
way is to add slots to base operation classes as only those properties do get passed into dependency operations.
There is a more simple way pass arguments from operate to operation functions - by means of key arguments!

The :do-first initarg is actually ignored by ASDF - its always set to ((compile-op (load-op ,@depends-on))))

Avoid inline methods, which are rather inelegant in ASDF:
- they rely on eval,
- ASDF tries to remove a method from a generic function of a different name.
Due to non-standard behavior of remove-method in LW 4.4, system
redefinition intrusively signals about this.

Referring to features in component definition is more useful than for dependency rules.